Sendmail is a Mail Transfer Agent, which is the
program that moves mail from one machine to
another. Sendmail implements a general
internetwork mail routing facility, featuring
aliasing and forwarding, automatic routing to
network gateways, and flexible configuration.

RPL/2 (Reverse Polish Lisp/2) is a langage derived from the RPL made by Hewlett-Packard for its HP-28S. It has some extensions (preprocessor, compilated libraries, new functions), a TeX output, and can draw graphics.

Monit is a utility for managing and monitoring processes, programs, files, directories, and devices on a Unix system. It conducts automatic maintenance and repair and can execute meaningful causal actions in error situations. It can be used to monitor files, directories, and devices for changes, such as timestamps changes, checksum changes, or size changes. It is controlled via an easy to configure control file based on a free-format, token-oriented syntax. It logs to syslog or to its own log file and notifies users about error conditions
via customizable alert messages. It can perform various TCP/IP network checks, protocol checks, and can utilize SSL for such checks. It provides an HTTP(S) interface for access.

tinc is a Virtual Private Network (VPN) daemon that uses tunneling and encryption to create a secure private network between multiple hosts on the Internet. This tunneling allows VPN sites to share information with each other over the Internet without exposing any information.

Monitorix is a lightweight system monitoring tool designed to monitor as many services and system resources as possible. It has been created to be used under production Linux/UNIX servers, but due to its simplicity and small size may also be used on embedded devices as well.

Performance Co-Pilot (PCP) is a framework and set of services for supporting system-level performance monitoring and performance management. It provides a unifying abstraction for all of the interesting performance data in a system, and allows client applications to easily retrieve and process any subset of that data using a single API. A client-server architecture allows multiple clients to monitor the same host, and a single client to monitor multiple hosts. Archive logging and replay are integrated so that a client application can use the same API to process real-time data from a host or historical data from an archive.

Dar is a shell command that makes backup of a directory tree and files. Its features include splitting archives over several files, DVD, CD, ZIP, or floppies, compression, full or differential backups, strong encryption, proper saving and restoration of hard links, extended attributes, file forks, Door inodes, and sparse files, remote backup using pipes and external commands (such as ssh), and rearrangement of the "slices" of an existing archive. It can run commands between slices, before and after saving some defined files or directories (for a proper database backup, for example), and quickly retrieve individual files from differential and full backups. Several external GUIs exist as alternatives to its CLI interface, like kdar, DarGUI, SaraB, etc.

pv (Pipe Viewer) is a terminal-based tool for monitoring the progress of data through a pipeline. It can be inserted into any normal pipeline between two processes to give a visual indication of how quickly data is passing through, how long it has taken, how near to completion it is, and an estimate of how long it will be until completion.

KBACKUP is intended for handling of backups no
matter whether they reside on disk or tape or even
in files. As most other backup programs available
today are either confusing the user with lots of
long command line options, or user friendly but not
powerful at all, the aim behind writing KBACKUP was
to provide a user friendly yet powerful backup
program. It is also intended to be kept compatible
to existing and well proven archive formats, so you
can restore your archives even if you should not
have KBACKUP around anymore.